St. Catherine of Siena was the youngest of the twenty-five children of Giacomo di Benincasa, a dyer, and was born, with a twin sister who did not survive her birth, on the 25th of March 1347. A highly sensitive and imaginative child; she very early began to practice asceticism and see visions, and at the age of seven solemnly dedicated her virginity to Jesus Christ. She was attracted by what she had heard of the desert anchorites, and in 1363-64, after much struggle, persuaded her parents to allow her to take the habit of the Dominican tertiaries. For a while she led at home the life of a recluse, speaking only to her confessor, and spending all her time in devotion and spiritual ecstasy. Her innate humanity and sound sense, however, led her gradually to return to her place in the family circle, and she began also to seek out and help the poor and the sick. In 1368 her father died, and she assumed the care of her mother Lapa. During the following years she became known to an increasingly wide circle, especially as a peacemaker, and entered into correspondence with many friends. Her peculiarities excited suspicion, and charges seem to have been brought against her by some of the Dominicans to answer which she went to Florence in 1374, soon returning to Siena to tend the plague-stricken. Here first she met the Dominican friar, Raimondo of Capua, her confessor and biographer.

The year 1375 found Catherine entering on a wider stage. At the invitation of Piero Gambacorti, the ruler of the republic of Pisa, she visited that city and there endeavored to arouse enthusiasm for the proposed crusade, urging princes and presidents, commanders and private citizens alike to join in "the holy passage." To this task was added that of trying to keep Pisa and Lucca from joining the Tuscan League against the pope. It was at Pisa, in the church of Santa Cristina, on the fourth Sunday in Lent (April 1), while rapt in ecstasy after the communion, that Catherine's greatest traditional glory befell her, the stigmata or impression on her hands, feet and heart, of the wounds corresponding with those received by Christ at his crucifixion. The marks, however, were at her prayer not made visible. There is no need to doubt the reality of Catherine's exaltation, but it should be remembered that she and her circle were Dominicans, and that the stigmata of St. Francis of Assisi were considered the crowning glory of the saint, and hitherto the exclusive boast of the Franciscans. The tendency observable in many of the austerities and miracles attributed to St. Catherine to outstrip those of other saints, particularly Francis, is especially remarkable in this marvel of the stigmata, and so acute became the rivalry between the two orders that Pope Sixtus IV, himself a Franciscan, issued a decree asserting that St. Francis had an exclusive monopoly of this particular wonder, and making it a censurable offence to represent St. Catherine receiving the stigmata.

In the year 1376, the 29th of Catherines life, Pope Gregory XI was living and holding the papal court at Avignon. He was the last of seven French popes in succession who had done so, and had perpetuated for seventy-three years what ecclesiastical writers are fond of terming "the Babylonian captivity of the church." To put an end to this absenteeism, and to bring back the papacy to Italy was the cherished and anxious wish of all good Italians, and especially of all Italian churchmen. Petrarch had urgently pressed Pope Urban V, Gregory's immediate predecessor, to accomplish the desired change; and Dante had at an earlier date labored to bring about the same object. But these and all the other influences which Italy had striven to bring to bear on the popes had hitherto failed to induce them to return. In these circumstances Catherine determined to try her powers of persuasion and argument, attempting first by correspondence to reconcile Gregory and the Florentines, who had been placed under an interdict, and then going in person as the representative of the latter to Avignon, where she arrived on the 18th of June. Gregory empowered her to treat for peace, but the Florentine ambassadors were first tardy and then faithless. Nothing daunted, Catherine herself besought Gregory, who, indeed, was himself so minded, to return, and he did so, in September (taking the sea route from Marseilles to Genoa), though perhaps intending only to make a temporary stay in Italy. Catherine went home by land and stayed for a month in Genoa with Madonna Orietta Scotti, a noble lady of that city, at whose house Gregory had a long colloquy with her, which encouraged him to push on to Rome. To this year, 1376, belongs the admission to Catherine's circle of disciples of Stefano di Corrado Maconi, a Sienese noble distinguished by a character full of charm and purity, and her healing of the bitter feud between his family and the Tolomei. Another family quarrel, that of the Salimbeni at Rocca D'Orcia, was ended by her intervention in 1377. This year. also she turned the castle of Belcaro, which had been given to her, into a monastery.

Meanwhile the returned pope was not having an easy time. Besides perpetuating the strife with his enemies he was alienating his friends, and finding it increasingly difficult to pay his mercenaries. He vented his anger upon Catherine, who reproved him for minding temporal rather than spiritual things, but in the beginning of 1378 sent her on an embassy to Florence and especially to the Guelph party. While she was urging the citizens to make peace with the pope there came the news of his death. During the troubles that ensued in Florence Catherine nearly lost her life in a popular tumult, and sorely regretted not winning her heart's desire, "the red rose of martyrdom." Peace was signed with the new Pope Urban VI, and Catherine, having thus accomplished her second great political task, went home again to Siena. From there on the outbreak of the schism Urban summoned her to Rome, where, somewhat reluctantly, she journeyed with her now large spiritual family in November. Once arrived she gave herself heartily to Urban's cause, and wore her slender powers out in restraining his impatient temper, quieting the revolt of the people of Rome, and trying to win for Urban the support of Europe. After prolonged and continual suffering she died on the 29th of April 1380.

Catherine of Siena lived on not only in her writings but in her disciples. During her short course she gathered around her a devoted company of men and women trained to labor for the reformation of the individual, the church and the state. Her death naturally broke up the fellowship, but its members did not cease their activity and kept up what mutual correspondence was possible. Among them were Fra Raimondo, who became master-general of the Dominicans, William Flete, an ascetically-minded Englishman from Cambridge, Stefano Maconi, who joined the Carthusians and ultimately became prior-general, and the two secretaries, Neri di Landoccio and Francesco Malavoiti. The last of her band, Tommaso Caffarini, died in 1434, but the work was taken up, though in other shape, by Girolamo Savonarola, between Francis of Assisi and whom Catherine forms the connecting link.

Catherine's works consist of (1) a treatise occupying a closely-printed quarto volume, which Fra Raimondo describes as "a dialogue between a soul, which asked four questions of the Lord, and the same Lord, who made answer and gave instruction in many most useful truths", (2) letters, and (3) prayers. The dialogue is entitled, The Book of Divine Doctrine, given in person by God the Father, speaking to the mind of the most glorious and holy virgin Catherine of Siena, and written down as she dictated it in the vulgar tongue, she being the while entranced, and actually hearing what God spoke in her. The work is declared to have been dictated by the saint in her father's house in Siena, a little before she went to Rome, and to have been completed on the 13th of October 1378. The book opens with a passage on the essence of mysticism, the union of the soul with God in love, and the bulk of it is a compendium of the spiritual teachings scattered throughout her letters. There is more monologue than dialogue. The book has a significant place in the history of Italian literature. "In a language which is singularly poor in mystical works it stands with the Divina Commedia as one of the two supreme attempts to express the eternal in the symbolism of a day, to paint the union of the soul with the supra-sensible while still imprisoned in the flesh." The prayers (twenty-six in all) are mostly mystical outpourings repeating the aspirations found in her other writings. Of more interest are the letters, nearly four hundred in number, and addressed to kings, popes, cardinals, bishops, conventual bodies, political corporations and private individuals. Their historical importance, their spiritual fragrance and their literary value combine to put their author almost on a level with Petrarch as a 14th century letter-writer. Her language is the purest Tuscan of the golden age of the Italian vernacular, and with spontaneous eloquence she passes to and fro between spiritual counsel, domestic advice and political guidance.